New directions in nano-optomechanics

The interaction between light and mechanical motion is boosted in lightweight nanoscale resonators. After landmark optomechanics experiments realized on single resonators, the investigation of collective phenomena now requires controlling vast ensembles of resonators, coupled by light or vibrations. The evolution towards collective nano-optomechanics bears potential for a variety of sensing applications as well as for quantum or topological photonics. It is however impeded by the disorder imposed by nanofabrication techniques, which naturally detunes high-Q resonators and precludes resonant interactions amongst them.
Here we present a new technique to resonantly tune ensembles of nanophotonic/mechanical resonators, building on the recent experimental development of nano-optomechanics in liquids [1]. Laser light injected into the optical mode of a resonator immersed in a fluid triggers an adjustable etching process, leading to fine-tuning of the resonator dimensions with picometer precision.
This process is naturally scalable to multiple resonators and has allowed us to resonantly tune small ensembles (2 to 5 units) [2]. As a first application, we explore the resonant optical interaction of multiple and distant nano-optomechanical systems. Light flowing unidirectionally along a (chiral) chain of nano-optomechanical oscillators is observed to produce their frequency locking above a certain threshold, a first example of collective phenomenon in optomechanics [3]. Our experiments are explained by a minimal semi-classical model, and set the grounds for more advanced quantum experiments.
 
[1] Gil-Santos, E., et al. High-frequency nano-optomechanical resonators in liquids, Nature Nanotechnology 10, 810 (2015)
[2] Gil-Santos, E., et al. Scalable high-precision tuning of photonic resonators by resonant cavity-enhanced photoelectrochemical etching, Nature Communications 8, 14267 (2017).
[3] Gil-Santos, E., et al. Light-mediated cascaded locking of multiple nano-optomechanical oscillators, Phys Rev Lett 118, 063605 (2017).